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Chapter Five

The unique construction of wool felt permits it to be worked by simple methods; and with economy, since edges cut clean, yet will not ravel nor fray.

Felt cutting plants have developed many original methods of working felt, fabricating mechanical parts and fortifying them by means of special treatments.

Experience aids these plants in the cooperative solution of many customers’ problems in the design of parts of which felt is an ingredient.

Wool felt chiefly owes its extensive application throughout the wide field of industrial design to the unique principal that the fibres composing it are interlocked in every direction. Because of this characteristic, felt can be cut at any angle with respect to the piece without the slightest possibility that it will ravel or fray. What is more, the through-bondage between the surfaces of a piece of felt is so uniform that cut felt parts exhibit no tendency to separate into layers, despite the laminar formation of the batt from which the material was fabricated. Splitting resistance, which measures the interfacial strength of felt, is increased in proportion to the density of the material. Although definite laminations are apparent in the softer qualities, the harder grades exhibit a progressively finer grain structure. Sheet felts are practically amorphous.

This is proved by the rapidly growing use of “rockhard” felt in grinding wheels and bobs, which would wear unevenly and soon become valueless if strongly marked by a laminated or grained composition. Thus the very hard felts are commonly turned in a speed-lathe and surfaced with sandpaper. Other grades are forced through dies to form endless wicks from 1/16 inch diameter and upward used for electric razor lubrications, up to a diameter of one inch for farm tractor oilers. Die-cut gaskets of intricate contour are often specified with rectangular cross-sections no more than 1/8 inch square and pierced with holes for screws or locating dowels no more than 1/32 inch from an edge, in a thickness of approximately 1/8 inch. Not only can felt be cut in any direction, but when subjected to wear, it wear through without change of frictional resistance, or any other specified property, since it is not “cased” by hardening and fulling, nor reinforced with warp and filler strands, like cloth. Felt surfaces, therefore, can never become threadbare.

Mechanical felts were originally stamped to the required shapes by consumers, but obviously the more critical applications demand expert knowledge of the material in all qualities and densities. Hence the manufacturers found themselves consulted increasingly by their customers, and eventually felt cutting became a business in itself which is operated independently in some instances, and in others as a division of the producing mills. The American Felt cutting plants at Glenville, Conn., Detroit, Mich., and San Francisco, Cal., are devoted exclusively to the design and fabrication of engineered felt parts. Many of these, such as washers and gaskets, are turned out in enormous quantities, and also in great variety of intricate shapes, often for odd and interesting purposes. Economic considerations have fostered the development of the felt cutting plant in several ways. Primarily, the selection of the most suitable quality of material for a given purpose, and also the best method of forming it with cutting dies designed for the density and character of the felt is better understood by the manufacturer’s own cutting division than by the consumer.

From its wide experience in catering to many different industries, the cutting plant has developed many short-cuts, including tools, machinery and methods. Multiple dies and gang dies speed production, while the matching of orders for differently shaped parts permits the most economical utilization of the goods. The principle applies directly to all such simple methods as shearing, punching, die-cutting, skiving, turning, grinding, and so on. It applies even more importantly in the fabrication of composite parts and the working of treated felts. Several pieces of different shape and quality felt are often united in a single part by stitching, riveting or the application of adhesives. Felt is frequently combined with other materials, then shaped to serve specific purposes.

Mechanical felt parts leave the cutting plants ready for use, in many instances going directly to the consumer’s assembling department in step with the production schedule. This is a great convenience, especially for plants having a high production rate, or where manufacturing space is at a premium. This service goes beyond expert choice of materials and economical fabrication to include the adaptation of felt to many uses for which its aptitude has not been obvious. American Felt Company engineers have carried out important development work on design-problems in many different industrial lines. They have also done pioneer work on specifications and testing methods in the study of adhesives and in special treatments which extend or improve the natural properties of felt.